Workpiece singulator with adjustable stair depth

ABSTRACT

Embodiments of the present disclosure provide a workpiece singulator with one or more movable stairs. A first one of the movable stairs may include an outer step member and an inner step member that is positioned between the outer step member and a second one of the movable stairs. The step members may be movable synchronously as a single stair to transport larger workpieces and asynchronously to transport smaller workpieces on the outer step member. Optionally, the workpiece singulator may further include a sensor configured to detect the size and/or position of a workpiece. In some embodiments, the workpiece singulator may be coupled with a controller configured to control the position of the outer step member independently of the position of the inner step member. In various embodiments, a workpiece singulator as disclosed herein may be operable to selectively singulate workpieces of different sizes.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 15/153,045, filed May 12, 2016, which is a continuation of U.S.patent application Ser. No. 14/710,316, filed May 12, 2015, which claimsthe benefit of U.S. Patent Application No. 61/992,740, filed May 13,2014, all titled “WORKPIECE SINGULATOR WITH ADJUSTABLE STAIR DEPTH,” theentire disclosures of which are incorporated by reference herein.

BACKGROUND

Step feeders are used to singulate and transfer workpieces from onelocation to another. Some step feeders include moving stairs interposedbetween fixed stairs, with the moving stairs driven by a motor and crankshaft. A log, cant, or other workpiece is deposited onto the lowest ofthe moving stairs, and the moving stair is driven upward to lift theworkpiece to a fixed stair. The next moving stair lifts the workpiecefrom the fixed stair to the next consecutive fixed stair, and so on,until the workpiece reaches the desired location. Other step feedershave two sets of moving stairs. In step feed feeders of this type, oneset of moving stairs is moved up while the other set is moved down.

In both cases, the moving stair that raises the workpiece has a fixeddepth. Shallow stairs are suitable for singulating small workpieces, butlarger workpieces may fall off the stairs during transport. Deeperstairs are more useful for singulating larger workpieces, but they mayallow smaller workpieces to be carried on the moving stair in groups oftwo or more, making the stairs less suitable for singulating smallworkpieces.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. Embodimentsare illustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIGS. 1A-1B illustrates a schematic side view of a workpiece singulatorwith variable stair depth;

FIGS. 2A-2B illustrate schematic side views of operations of a workpiecesingulator with variable stair depth;

FIG. 3 illustrates a schematic side view of movable stair ranges;

FIGS. 4A-4B illustrate schematic side views of workpiece singulatorsystems; and

FIGS. 5A-5D illustrate schematic side views of workpiece singulatorsystems, all in accordance with various embodiments.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which are shownby way of illustration embodiments that may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope. Therefore,the following detailed description is not to be taken in a limitingsense, and the scope of embodiments is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments;however, the order of description should not be construed to imply thatthese operations are order dependent.

The description may use perspective-based descriptions such as up/down,back/front, and top/bottom. Such descriptions are merely used tofacilitate the discussion and are not intended to restrict theapplication of disclosed embodiments.

The terms “coupled” and “connected,” along with their derivatives, maybe used. It should be understood that these terms are not intended assynonyms for each other. Rather, in particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalor electrical contact with each other. “Coupled” may mean that two ormore elements are in direct physical or electrical contact. However,“coupled” may also mean that two or more elements are not in directcontact with each other, but yet still cooperate or interact with eachother.

For the purposes of the description, a phrase in the form “A/B” or inthe form “A and/or B” means (A), (B), or (A and B). For the purposes ofthe description, a phrase in the form “at least one of A, B, and C”means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).For the purposes of the description, a phrase in the form “(A)B” means(B) or (AB) that is, A is an optional element.

The description may use the terms “embodiment” or “embodiments,” whichmay each refer to one or more of the same or different embodiments.Furthermore, the terms “comprising,” “including,” “having,” and thelike, as used with respect to embodiments, are synonymous.

Embodiments of methods, apparatuses, and systems for singulatingworkpieces are provided herein. In various embodiments, the workpiecesmay be logs, cants, boards, or other such items. In exemplaryembodiments, a computing device may be endowed with one or morecomponents of the disclosed apparatuses and/or systems and may beemployed to perform one or more methods as disclosed herein.

Embodiments of the present disclosure provide a workpiece singulatorwith a set of movable stairs. In various embodiments, a workpiecesingulator may have a first, a second, and a third movable stair. Eachof the movable stairs may have a corresponding positioning range. Theupper end of the range may be represented by an extended position, andthe lower end of the range may be represented by a retracted position.Optionally, the positioning ranges of consecutive movable stairs maymeet or overlap one another. For example, when the first movable stairis in the extended position and the second movable stair is in theretracted position, the workpiece support surfaces of the first andsecond movable stairs may define an inclined plane. Similarly, when thesecond movable stair is in the extended position and the third movablestair is in the retracted position, the workpiece support surface of thesecond and third movable stairs may define another inclined plane.Workpieces may be moved upwardly on one movable stair onto the nextconsecutive movable stair.

In various embodiments, a first one of the movable stairs may include afirst step member and a second step member. The first and second stepmembers may be coupled with corresponding drives that are independentlyoperable to drive the first step member independently of the second stepmember. One or more of the other movable stairs may also include two ormore step members that are movable independently of one another.

In some embodiments, one or both of the drives may be selectivelyoperable in a first mode and in a second mode. In the first mode, thesecond step member may be driven synchronously with the first stepmember, such that the step members collectively function as the movablestair, and the effective stair depth of the movable stair is equal tothe combined depths of the step members. In the second mode, the secondstep member may be driven asynchronously (e.g., with the second stepmember remaining stationary), such that the first step member functionsas that movable stair, and the effective depth of that movable stair isequal to the depth of the first step member. Optionally, while operatingin the second mode the second step member may be positioned at the sameor similar level as the next consecutive stair/step member.

In various embodiments, the first and second step members may be (or mayinclude) platforms that are independently movable. The first step membermay be the “outer” first platform of the movable stair and the secondstep member may be the “inner” second platform of the movable stair.Thus, the second step member may be disposed between the first stepmember and the next consecutive movable stair. In some embodiments, themovable stair may include one, two, three, or more than three additionalplatforms between the first step member and the second step member. Thefirst, second, and/or additional platforms may have correspondingworkpiece support surfaces, such as the top end surfaces of theplatforms. Optionally, one or more of the additional platforms may becoupled with a corresponding drive configured to move the additionalplatform(s) independently of the first and second platforms. In someembodiments the workpiece singulator may have one or more additionalmovable stairs that include corresponding first, second, and/oradditional step members.

In various embodiments, the step members may have workpiece supportsurfaces that are inclined relative to a horizontal plane, such that thedistal end of the workpiece support surface is elevated relative to theproximal end of the workpiece support surface. The inclined angle of theworkpiece support surfaces may help to prevent accidental dislocation ofthe workpieces from the stairs due to gravity and aid the movement ofthe workpieces toward the next consecutive stair and/or the deliverylocation. Likewise, the supply location may be inclined to encouragemovement of the workpieces onto the bottom-most stair. As a workpiece ona movable stair reaches the next consecutive stair, the workpiece mayslide toward the proximal end of the workpiece support surface and ontothe next consecutive stair.

In various embodiments, the step members of a movable stair may bedriven independently of one another. For example, the first and secondstep members of a movable stair may be driven independently by a driveassembly that includes a first drive coupled with the first step memberand a second drive coupled with the second step member. In someembodiments, each of the step members of two or more movable stairs mayhave a corresponding drive and be driven independently of the other stepmembers. Alternatively, in other embodiments each of the step members ofa movable stair may be driven independently of one another, but inconcert with the corresponding step member(s) of another one or more ofthe movable stairs. For example, the first step member of one movablestair and the first step member of another movable stair may be drivenby the first drive, and the second step members of those movable stairsmay be driven by a second drive. In such embodiments, the first stepmembers may be linked, such as by a beam, skid, or other type ofsupport, and the second step members may be linked in the same orsimilar manner. The first and second drives may be coupled with thelinkage to drive the corresponding step members. Optionally, the linkmay be adjustable and/or removable to allow separate actuators to becoupled with some or all of the step members.

In some embodiments, the workpiece singulator may include a controllerthat is configured to control the drive assembly and drives thereof. Inother embodiments, the workpiece singulator may include a sensor coupledwith the controller and configured to detect the presence and/or size ofa workpiece on or near the movable stairs. Optionally, the controllermay include a programmable logic controller (PLC), a computer, or both.For example, the controller may include a computing device endowed withinstructions that are operable, upon execution by a processor, to causethe computing device to send instructions to the controller based atleast on data from the sensor.

In operation, a movable stair or one or more of the step members thereofmay be driven along a reciprocating path from a first level (e.g., aworkpiece loading level) to a next consecutive second level (e.g., thelevel of the next consecutive step member or movable stair). In variousembodiments, the step members may be moved independently of one another,such that the step members of a movable stair can be repositioned eithersynchronously or asynchronously as desired. This may allow the workpiecesingulator to be used in one mode to singulate larger workpieces and inanother mode to singulate small workpieces (e.g., by using only thefirst step member of the movable stair to receive and transport theworkpiece to a next level). In some embodiments, a portion of theworkpiece singulator may be operable in one mode while another portionof the workpiece singulator is operable in the other mode. For example,the bottom-most movable stair(s) may be operated synchronously to liftlarge or multiple small workpieces, and the upper-most movable stair(s)may be operated asynchronously to singulate the workpieces and/or removeworkpieces exceeding a particular size.

In various embodiments, one or more workpieces may be delivered to aloading area. One or more of the step members of the first movable stairmay be moved downwardly to the retracted position to engage one of theworkpieces on the support surfaces of the step member(s). The stepmember(s) may be driven upwards toward the extended position. As theworkpiece is raised on the support surface(s) of the step member(s), theworkpiece may be supported against the outer surface of the nextconsecutive step member(s) until the workpiece reaches the supportsurface of the next consecutive step member(s). The inclined angle ofthe support surfaces may help the workpiece to slide or roll onto thesupport surface of the next consecutive step member(s), which will raisethe workpiece to the next level, and so on, until the workpiece reachesthe delivery location.

In various embodiments, the receiving location of the step feeder may beat any height relative to the delivery location of the step feeder (thatis, where the step feeder discharges or delivers singulated workpieces).For example, in some embodiments, the receiving location and thedelivery location may be at the same height relative to the ground. Inother embodiments, the receiving location may be at a different heightthan the delivery location, such as higher or lower than the deliverylocation.

FIGS. 1A-1B illustrate side views of a workpiece singulator withvariable stair depth, and FIGS. 2A-2B illustrate schematic side views ofoperations of a workpiece singulator with variable stair depth, all inaccordance with various embodiments.

Referring first to FIGS. 1A-2A, workpiece singulator 100 may include aframe 102 with a set of movable stairs. Each of the movable stairs mayinclude two or more step members. In the illustrated embodiment, a firstmovable stair includes a first step member 104 and a second step member106, a second movable stair includes a third step member 108 and afourth step member 110, and a third movable stair includes a fifth stepmember 112 and a sixth step member 114. However, in other embodiments amovable stair may have only one step member or three or more stepmembers.

In various embodiments, workpiece singulator 100 may be operable in onemode to singulate relatively large workpieces 2 (see e.g., FIGS. 1A and2A) and in another mode to singulate smaller workpieces 4 (see e.g.,FIGS. 1B and 2B). While workpieces 2 and 4 are illustrated as logs, itis to be understood that workpiece singulators as described herein mayalso be used to singulate other workpieces such as cants, boards,flitches, stems, or other such items.

As shown for example in FIGS. 1A and 2A, in one mode the step members ofa movable stair may be used synchronously as a unit to move largeworkpieces from one level to another. As shown for example in FIGS. 1Band 2B, in another mode the step members of a movable stair may bemoved/positioned asynchronously to move smaller workpieces. In someembodiments, the outer-most step may be moved between the retractedposition and the extended position of that movable stair. Alternatively,the first/outer-most step may be moved between the retracted positionand an intermediate position (e.g., one half or one third of the rangeof that movable stair) and the second/inner-most step may be movedbetween the extended position and the same or other intermediateposition, as shown for example in FIG. 2B, to transport a smallerworkpiece to the next consecutive stair.

FIG. 3 illustrates a schematic diagram of movable stair ranges, inaccordance with various embodiments. The movable stairs may be operatedto move workpieces (e.g., workpieces 2 and/or 4) from a loading area 126to a destination area 116. In the illustrated embodiment, each of thestep members 104, 106, 108, 110, 112, and 114 are movable between aretracted position (shown in dashed lines) and an extended position. Theworkpiece support surfaces of step members 104 and 106 are at a firstlevel 118 while in the retracted position, and at a second level 120while in the extended position. The workpiece support surfaces of stepmembers 108 and 110 are at the second level 120 while in the retractedposition, and at a third level 122 while in the extended position. Theworkpiece support surfaces of step members 112 and 114 are at the thirdlevel 122 while in the retracted position, and at a fourth level 124while in the extended position.

FIGS. 4A-4B and 5A-5C illustrate schematic side views of workpiecesingulator systems, all in accordance with various embodiments. In someembodiments, a controller 130 may be operatively coupled with, andconfigured to control the positions of, the movable stairs/step members.Optionally, one or more sensors 128 may be operatively coupled withcontroller 130, and controller 130 may be configured to control thepositions of one or more of the step members based at least on data fromthe sensor(s) 128. Sensor(s) 128 may include, but is not limited to, oneor more photo-eyes, cameras, scanners, or any other devices suitable fordetecting a position and/or size of a workpiece.

In various embodiments, as shown for example in FIGS. 5A-D, an actuator132 may be coupled with one or more of the step members, and controller130 may be operatively coupled with actuator(s) 132. Again, one or moresensor(s) 128 may be coupled with controller 130.

In some embodiments, a first actuator 132 may be coupled with eachouter-most step member (e.g., step members 104, 108, and 112) andconfigured to control those step members, and a second actuator 132 maybe coupled with each inner-most step member (e.g., step members 106,110, and 114) and configured to control those step members independentlyof the outer-most step members. Controller 130 may be configured tocontrol the first and second actuators 132 to move the step members ofeach movable stair in unison (e.g., step members 104 and 106 movedtogether, step members 108 and 110 moved together, and step members 112and 114 moved together) to move larger workpieces. Controller 130 mayalso be configured to control the first and second actuators 132 to movethe outer-most step members of each stair asynchronously with thecorresponding inner-most step members to move smaller workpieces.

In other embodiments, as shown for example in FIG. 5C, some or all ofthe step members may be independently coupled with correspondingactuators 132. Controller 130 may be coupled with, and configured tocontrol, each of the actuators 132. Optionally, controller 130 may beconfigured to determine, based on data from sensor 128, which of the twomodes to use. For example, controller 130 may be configured todetermine, based on data from sensor 128, that some or all of theworkpieces in loading area 126 are smaller workpieces. In response tothe determination, controller 130 may operate the workpiece singulatorin the small workpiece mode, such that the step members of a movablestair are moved asynchronously. Controller 130 may also be configured todetermine, based on data from sensor 128, that some or all of theworkpieces in loading area 126 are larger workpieces. In response to thedetermination, controller 130 may operate the workpiece singulator inthe large workpiece mode, such that the step members of a movable stairare moved synchronously as a single unit. Alternatively, controller 130may be configured to operate the workpiece singulator in response toinput/control by a human operator. For example, controller 130 may beconfigured to operate the workpiece singulator in a mode selected by ahuman operator, or may have one or more controls usable by a humanoperator to control one or more of the step members/movable stairs.

In some embodiments, actuators 132 may be (or may include) hydraulic,pneumatic, and/or electric positioning cylinders. In other embodiments,actuators 132 may include rotary actuators with linkages configured toconvert rotary motion to linear motion (e.g., crankshafts driven byelectric drives or other types of drives). The number, type, andarrangement of actuators 132 may vary among embodiments, and anysuitable type of actuators known in the art may be used to drive thestep members.

The controller 130 may be configured to selectively operate the stepmember(s) of one or more of the movable stairs in a small workpiece modeand in a large workpiece mode. In the large workpiece mode, controller130 may be configured to move all of the step members of a given movablestair together as a single unit to support and raise a relatively largeworkpiece. In the small workpiece mode, controller 130 may be configuredto move fewer than all of the step members of a given movable stair(e.g., only the outer-most step member) to support and raise a smallerworkpiece. Optionally, the controller 130 may be configured to operatethe outer-most step member of a movable stair to engage and raise thesmaller workpiece along part of the range of that movable stair (e.g.,from first level 118 to half or one-third the distance between firstlevel 118 and second level 120), and to operate the inner-most stepmember to engage and raise the workpiece the remaining distance to thenext level (e.g., to second level 120). Alternatively, controller 130may be configured to operate the outer-most step member of a movablestair to engage and raise the smaller workpiece from one level (e.g.,first level 118) to the next level (e.g., second level 120).

In various embodiments, the workpiece singulator may be operable in acombination mode, in which the step members of at least one of themovable stairs are operated synchronously (as in large workpiece mode)while the step members of other movable stairs are operatedasynchronously and/or independently (as in small workpiece mode). Anembodiment of a workpiece singulator operating in combination mode isshown in FIG. 5D. In some embodiments, operating in combination modeinvolves operating the step members of the bottom-most movable stair(s)in large workpiece mode while operating the step members of theremaining movable stair(s) in small workpiece mode. This may allow thebottom-most movable stair to collect and raise multiple logs (e.g., froma log pile) in a single pass. Optionally, one or more of the othermovable stairs may also be operated in large workpiece mode tofacilitate the removal of any logs that were not stably positioned onthe bottom-most stair (e.g., a log that was resting on other logs on thestair), allowing them to fall back onto the bottom-most stair or ontothe pile of logs. The upper-most movable stair(s) operating in small logmode may singulate the logs. Operating the workpiece singulator incombination mode may help to provide a more constant rate of workpieceflow (e.g., by reducing the number of empty movable stairs) and/orreduce the risk of damage to the workpieces (e.g., by encouragingunstable workpieces to fall before they the upper movable stairs).

In other embodiments, controller 130 may be configured to control thestep members based at least in part on data from sensor 128 and/or inputfrom a human operator. For example, controller 130 may be configured toaccept an input from a human operator that indicates a desired log sizerange (e.g., smaller logs or larger logs), and control the step membersaccording to the corresponding mode. As another example, controller 130and/or actuators 132 may be configured to be directly controlled by ahuman operator, such as by way of one or more buttons, switches, orother types of input controls.

In some embodiments, the workpiece singulator may be configured to moveworkpieces onto the destination area 116 (e.g., a delivery platform,conveyor, or bin) one at a time. In other embodiments, controller 130may be selectively operable to move smaller workpieces onto thedestination area 116 either one at a time (e.g., in small workpiecemode) or two or more at a time (e.g., in large workpiece mode).

Although certain embodiments have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that a widevariety of alternate and/or equivalent embodiments or implementationscalculated to achieve the same purposes may be substituted for theembodiments shown and described without departing from the scope. Thosewith skill in the art will readily appreciate that embodiments may beimplemented in a very wide variety of ways. This application is intendedto cover any adaptations or variations of the embodiments discussedherein. Therefore, it is manifestly intended that embodiments be limitedonly by the claims and the equivalents thereof.

What is claimed is:
 1. A workpiece singulator, comprising: a set ofmovable stairs, a first one of the movable stairs having a first stepmember with a first workpiece support surface and a second step memberwith a second workpiece support surface, the second step member beingdisposed between the first step member and a second one of the movablestairs, and the first and second step members being movable alonggenerally parallel paths, wherein the first one of the movable stairs isconfigured to transport a workpiece from a first level to a secondlevel, and the second one of the movable stairs is configured totransport the workpiece from the second level to a third level; and adrive assembly coupled with the set of movable stairs, the driveassembly selectively operable to move the first step memberindependently of the second step member.
 2. The workpiece singulator ofclaim 1, further including a controller coupled with the drive assembly,the controller configured to control the drive assembly to move thesecond step member relative to the first step member to transportworkpieces of a first size and to move the first and second step membersin unison to transport workpieces of a second size greater than thefirst size.
 3. The workpiece singulator of claim 2, wherein the driveassembly includes a first drive coupled with the first step member and asecond drive coupled with the second step member, the controlleroperable to control the first drive independently of the second drive.4. The workpiece singulator of claim 3, further including a sensoroperatively coupled with the controller and configured to detect theworkpieces, the controller operable to control the first and seconddrives based at least on data from the sensor.
 5. The workpiecesingulator of claim 2, wherein the first step member is a first platformand the second step member is a second platform.
 6. The workpiecesingulator of claim 5, the first one of the movable stairs furtherincluding an additional step member disposed between the first stepmember and the second step member.
 7. The workpiece singulator of claim6, the drive assembly further including an additional drive coupled withthe additional step member, wherein the controller is further configuredto control the drive assembly to move the additional step memberindependently of the first step member.
 8. The workpiece singulator ofclaim 3, wherein the second one of the movable stairs further includes athird step member and a fourth step member, and the third step member isdisposed between the second step member and the fourth step member. 9.The workpiece singulator of claim 8, the drive assembly furtherincluding a third drive coupled with the third step member andconfigured to move the third step member between the second level andthe third level.
 10. The workpiece singulator of claim 9, the driveassembly further including a fourth drive coupled with the fourth stepmember and configured to move the fourth step member between the secondlevel and the third level.
 11. The workpiece singulator of claim 10,wherein the controller is coupled with the third and fourth drives, thecontroller further configured to control each of the drivesindependently of the other drives.
 12. The workpiece singulator of claim8, wherein the first drive is operatively coupled with the first andthird step members and the second drive is operatively coupled with thesecond and fourth step members.
 13. The workpiece singulator of claim 9,wherein the third step member includes a third platform and the fourthstep member includes a fourth platform, and the third platform isdisposed between the first platform and the fourth platform.
 14. Theworkpiece singulator of claim 13, wherein the drive system isselectively operable to move each of the platforms independently of theother platforms.
 15. A method of singulating workpieces of varioussizes, the method comprising: providing a set of movable stairs, whereinat least a first one of the movable stairs includes a first step memberand a second step member that are movable along generally parallel pathsbetween a first level and a second level, the second movable stair ismovable between the second level and a third level, the second stepmember is disposed between the first step member and a second movablestair, and the first step member is movable independently of the secondstep member; moving at least the first step member to the first level toreceive a workpiece; transporting the workpiece from the first level tothe second level on at least the first step member; and transporting theworkpiece from the second level to the third level on the second movablestair, wherein the first step member is selectively operableindependently of the second step member to transport workpieces of afirst size from the first level to the second level, and wherein thefirst and second step members are selectively operable in unison totransport workpieces of a larger second size from the first level to thesecond level.
 16. The method of claim 15, wherein the method furtherincludes controlling the first and second step members based at least onthe size of the workpiece.
 17. The method of claim 16, whereincontrolling the first and second step members includes moving the firststep member relative to the second step member to transport a workpieceof the first size between the first level and the second level.
 18. Themethod of claim 16, wherein controlling the first and second stepmembers includes moving the first and second step members in unisonrelative to the second movable stair to transport a workpiece of thesecond size from the first level to the second level.
 19. The method ofclaim 15, further including moving the first step member downwardly tothe first level to receive a workpiece.
 20. The method of claim 16,further including detecting the size of the workpiece prior to movingthe first step member to the first level.
 21. The method of claim 15,wherein the first step member includes a first platform and the secondstep member includes a second platform, the second platform is disposedbetween the first platform and the second movable stair, andtransporting the workpiece from the first level to the second level onat least the first step member includes moving the first platformupwardly relative to the second movable stair.
 22. A movable stairsystem for transporting workpieces, the system comprising: a firstmovable stair having a first step member with a first workpiece supportsurface and a second step member with a second workpiece supportsurface, the first and second step members being movable along generallyparallel paths between a first level and a second level, wherein thefirst step is operable independently of the second step to transport aworkpiece on the first workpiece support surface from the first level tothe second level; a second movable stair configured to be movablebetween the second level and a third level, wherein the second movablestair is operable to receive the workpiece at the second level andtransport the workpiece to the third level; a drive system coupled withthe first movable stair and configured to move the first step memberindependently of the second step member; and a controller operativelycoupled with drive system and configured to control the drive system tomove the first and second step members, the controller selectivelyoperable to cause the drive system to move the first step and secondstep members asynchronously to singulate workpieces of a first size, andto move the first and second step members in unison to transportworkpieces of a larger second size.
 23. The system of claim 22, whereinthe first step member includes a first platform and the second stepmember includes a second platform, and the second step member isdisposed between the first step member and the second movable stair. 24.The system of claim 23, the drive system including a first drive coupledwith the first step member and a second drive coupled with the secondstep member, wherein the controller is further configured to control thefirst drive independently of the second drive.
 25. The system of claim23, wherein the second movable stair includes a third step member and afourth step member, and the third step member is disposed between thesecond step member and the fourth step member.
 26. The system of claim25, the drive assembly further including a third drive coupled with thethird step member and a fourth drive coupled with the fourth stepmember, the third and fourth drives configured to move the third andfourth step members, respectively, between the second level and thethird level.
 27. The system of claim 26, wherein the controller isfurther configured to control each of said drive assembliesindependently of the others of said drive assemblies.
 28. The system ofclaim 27, wherein the third step member includes a third platform andthe fourth step member includes a fourth platform, and the thirdplatform is disposed between the second platform and the fourthplatform.
 29. The system of claim 28, the first movable stair furtherincluding one or more additional platforms disposed between said firstand second platforms.
 30. The system of claim 25, wherein the firstdrive is operatively coupled with the first and third step members, andthe second drive is operatively coupled with the second and fourth stepmembers.